What is the effect of DAPABORT?

Answer

DAPABORT is intended as a last desperate attempt to regain control of a hung system, leaving a specific AP and its memory system in an unknown state. From the ARM Debug Interface v5 Architecture Specification:

"From a software perspective, this is a fatal operation. It discards any outstanding and pending transactions, and leaves the AP in an unknown state."

"Use this function only in extreme cases, when debug host software has observed stalled target hardware for an extended period."

A DAPABORT in a Cortex-M3 or Cortex-M4 may terminate not only a hung AP access but also a processor access to the memory system which is in progress and possibly hung at that time.